The present invention relates to an automatic device which can be used to depress the low frequency oscillation of a power system.
Fast excitation systems and regulators have been widely used on generators of power system to improve the operating quality and enlarge the output capability in remote power transmission. However since thyristors and other fast excitation control systems came into use, low frequency oscillation, which can affect the whole power system, might occur when the power angle of the generator reaches about 60 degree, thus becoming a technical problem of power system that needs to be solved.
In prior art, power system stabilizers (PSS) and optimal control excitation were used to depress the low frequency oscillation. If merely the measuring of voltage deviation is taken, the control effects of both measures would not be satisfactory and it is hard to depress the low frequency oscillation. Therefore, other variables that could reflect the steady state must be measured and used as additional feedback regulating variables. Generally speaking, the effect of PSS was not satisfactory while the optimal control was too complicated to realize, and both had the defects of difficult realization, distortions, low reliability, and complex measuring devices, etc.
There are many literatures and patents concerning the method of depressing the low frequency oscillation of power system, such as: USSR Pat. No. 546057, No. 410514, No. 468333, No. 449419, No. 546057, No. 658653, but none of them relate to the solution like that in the present invention.